Injection module and exhaust system having an injection module

ABSTRACT

An injection module ( 10 ) for injecting a reducing agent, urea (AdBlue), into the exhaust system ( 22 ) of an internal combustion engine ( 2 ) has at least two outlet openings ( 12 ) for discharging at least one reducing agent la primary stream ( 13 ), the outlet openings ( 12 ) being angled and spaced apart in such a way that the reducing agent primary streams ( 13 ) being discharged from the outlet openings ( 12 ) meet each other so that they largely, but not entirely overlap and thereby achieve a uniform distribution in the spray mist ( 11 ).

The invention relates to an injection module, in particular an injectionmodule for injecting a reducing agent into the exhaust system of aninternal combustion engine, and to an exhaust system fitted with aninjection module of this kind.

PRIOR ART

SCR technology (“selective catalytic reduction”) using a urea-containingliquid reducing agent (“AdBlue®”) has proven its worth in removingnitrogen oxides from the exhaust gases of diesel engines. In thisprocess, the liquid reducing agent, an aqueous urea solution, is sprayedinto the exhaust gas stream upstream of a reducing agent catalyst and,at the same time, finely atomized before the exhaust gas/reducing agentmixture is fed to the SCR catalyst.

In order to achieve a high nitrogen oxide conversion rate with theminimum reducing agent slip, the reducing agent must be distributed asuniformly as possible over the inlet area of the catalyst. Hitherto,this has been achieved either by means of a mixer mounted in the exhaustpipe or by means of a long mixing section between the point at which thereducing agent is metered in and the catalyst.

DE 44 17 238 A1 discloses a device for reducing nitrogen oxides in theexhaust gases of an internal combustion engine, having an inlet chamber,a hydrolysis catalyst, a deNOx catalyst and an oxidation catalyst, inwhich the inlet chamber, the hydrolysis catalyst, the deNOx catalyst andthe oxidation catalyst form a substantially cylindrical unit throughwhich the exhaust gas stream can flow in the sequence stated and thediameter of the inlet chamber exceeds the diameter of the hydrolysiscatalyst. This ensures that the exhaust gas mixed with a reducing agentin the inlet chamber enters the catalyst with a uniform distribution ofthe reducing agent and an exhaust gas flow density which is as uniformas possible over the cross section of the exhaust system.

DE 10 2010 039 079 A1 describes an injection device for injecting afluid into an exhaust system of an internal combustion engine, having afirst flow region, which is designed in such a way that the fluid flowssubstantially in a first direction of flow, which is parallel to a valveaxis, in the first flow region during operation; a valve plate, whichdelimits the first flow region downstream, wherein a valve opening whichhas a smaller cross section than the first flow region in a planeorthogonal to the valve axis is formed in the valve plate; and at leastone spray hole plate, which is formed downstream of the valve openingand has at least one injection hole, which is designed in such a waythat the fluid flows out of the injection hole in a second direction offlow during operation. Here, the second direction of flow has acomponent aligned in the direction of the valve axis.

In order to achieve the desired homogenization of the reducing agentwith the exhaust gas, a reducing agent spray mist (“reducing agentspray”) which is as flat as possible but as far as possible covers thefull area is required. In order to avoid unwanted deposits of thereducing agent in the exhaust system, only a limited quantity of thereducing agent must strike the walls of the exhaust system.

DE 10 2013 223 296 discloses an injection module for injecting areducing agent into the exhaust system of an internal combustion engine,having at least two outlet openings for dispensing a reducing agentprimary jet in each case. In this case, the outlet openings are designedin such a way that the reducing agent primary jets emerging through theoutlet openings meet in the exhaust system in order to produce a spraymist.

DISCLOSURE OF THE INVENTION

One object of the invention is to optimize the spray mist produced by ajet collision in the exhaust system and, in particular, to produce aspray mist (“spray”) which as far as possible covers the full area andhas a mass distribution which is as uniform as possible.

An injection module according to the invention for injecting a reducingagent into the exhaust system of an internal combustion engine has atleast two outlet openings for dispensing at least one reducing agentprimary jet in each case.

In this case, the outlet openings are formed in such a way that thereducing agent primary jets emerging through the at least two outletopenings do not meet over their full area but with only a partialoverlap in order to produce a spray mist in the exhaust system by meansof the collision.

The invention also comprises a method of injecting a reducing agent intothe exhaust system of an internal combustion engine, wherein the methodincludes injecting at least two reducing agent primary jets into theexhaust system in such a way that they do not meet over their full areabut with only a partial overlap in order to produce a suitable spraymist in the exhaust system.

In this way, a flat reducing agent spray mist covering the full area andhaving a very uniform mass distribution is produced through jetcollision in the exhaust system, said mist mixing in an optimum mannerwith the exhaust gases flowing through the exhaust system and thusallowing an effective reduction in pollutants with a low consumption ofreducing agent.

In order to implement the partially overlapping collision of thereducing agent primary jets in accordance with the invention, it ispossible, in particular, for the outlet openings to be arranged offsetand/or tilted relative to one another. By arranging the outlet openingsin a manner offset and/or tilted relative to one another, partiallyoverlapping collision of the reducing agent primary jets can be achievedin an effective manner and by simple means.

In one embodiment, the overlap is in a range of from 30% to 70%, inparticular in a range of from 40% to 60%, of the area of the primaryjets. An overlap in this range has proven particularly advantageous forthe production of a spray mist which is as uniform as possible.

In one embodiment, the outlet openings are less than 5 mm apart, inparticular less than 2 mm apart, ensuring that, from their respectiveoutlet opening to the point of collision, the primary jets are compactjets that have not yet broken down into individual droplets. If theprimary jets have already broken down into individual droplets,individual droplets repeatedly lack collision partners; collision istherefore optimized by compact jets.

In one embodiment, the outlet openings are formed in such a way that thereducing agent primary jets meet at an angle of more than 30° in orderto optimize the collision between the two primary jets and bring aboutoptimum atomization of the primary jets.

In one embodiment, the outlet openings are formed in such a way that thereducing agent primary jets meet after a free path length of less than10 mm, in particular of less than 5 mm, in order to avoid the primaryjets splitting into individual droplets before the point of collision.

The outlet openings preferably have a circular cross section since thejet diameter and the outlet angle of the jet are precisely defined inthe case of a circular cross section. However, the outlet openings canalso be formed with an oval cross section.

The invention also comprises a section of an exhaust system of aninternal combustion engine in which an injection module according to theinvention is provided.

In one embodiment, the section of the exhaust system has, in addition tothe injection module, a shielding plate, which is designed and arrangedin such a way that it prevents the spray mist from striking a wall ofthe exhaust system. Unwanted deposits of the reducing agent, which couldnegatively affect the flow properties in the exhaust system, are in thisway reliably prevented.

The shielding plate can have one or more openings, which allow a definedflow of the exhaust gases through the shielding plate in order toselectively influence the flow behavior of the exhaust gases in theexhaust system.

In one embodiment, the shielding plate is arranged in such a way that abuildup chamber is formed between the shielding plate and at least onewall of the exhaust system. During operation, an exhaust gas excesspressure arises in the buildup chamber, causing exhaust gases to flowthrough holes formed in the shielding plate, which results inparticularly effective mixing of the exhaust gases with the reducingagent atomized in accordance with the invention.

In one embodiment, an additional plate is arranged upstream of theinjection module to prevent the reducing agent spray mist from beingdispersed by the exhaust flow at the point of collision of the primaryjets and thus to ensure reliable production of a spray mist by theprimary jets.

In one embodiment, an oxidation catalyst is arranged upstream of theinjection module, and a reduction catalyst is arranged downstream of theinjection module, in order to ensure optimum exhaust gas purification.In particular, the injection module is arranged in a connecting ductwhich connects the outlet of the oxidation catalyst with the inlet ofthe reduction catalyst in terms of flow in order to feed the reducingagent to the exhaust gases directly ahead of the reduction catalyst.

In one embodiment, the direction of flow of the exhaust gases is changedby the connecting duct. This allows a particularly compact structuralshape of the exhaust system and brings about swirling of the exhaust gasflow. Such swirling of the exhaust gas flow results in particularlyeffective mixing of the exhaust gases with the reducing agent spraymist.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic sectional view of an exhaust system accordingto the invention.

FIG. 2 shows a schematic partially sectioned view of an injection moduleaccording to the invention.

FIG. 3a shows the collision of two primary jets which meet over theirfull area.

FIG. 3b shows a graphical representation of a spray mist of the kindproduced by the collision shown in FIG. 3 a.

FIG. 4a shows the collision of two primary jets which meet with a slightoverlap.

FIG. 4b shows a graphical representation of a spray mist of the kindproduced by the collision shown in FIG. 4 a.

FIG. 5a shows the collision of two primary jets 13 which meet with aconsiderable but not full overlap.

FIG. 5b shows a graphical representation of a spray mist of the kindproduced by the collision shown in FIG. 5 a.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic view of an internal combustion engine 2 havingan exhaust system 22.

Fresh air 7 a is fed into the cylinders 2 a-2 d of the engine 2 via acompressor 1 of a turbocharger 1, 3. The exhaust gases formed duringoperation in the cylinders 2 a-2 d pass through a turbine 3 of theturbocharger 1, 3, which drives the compressor 1, into an oxidationcatalyst 4 arranged downstream of the internal combustion engine 2.

In addition to the oxidation catalyst 4, there is a reducing agentcatalyst 6. This can be designed as an SCR catalyst 6 or as aparticulate filter with an SCR catalyst coating. The outlet of theoxidation catalyst 4 and the inlet of the reducing agent catalyst 6 areconnected to one another in terms of flow by a connecting duct 5, withthe result that the exhaust gases from the oxidation catalyst 4 flowthrough the connecting duct 5 into the reducing agent catalyst 6. Theexhaust gases 7 b purified by the catalysts 4, 5 emerge from thereducing agent catalyst 6 into the environment.

Mounted on the connecting duct 5 is an injection module 10 according tothe invention, which is supplied with a liquid reducing agent, inparticular an aqueous urea solution (“AdBlue®”), by a reducing agentmetering system, which is conventional and is therefore not shown indetail.

During operation, the injection module 10 produces a reducing agentspray mist 11 in the connecting duct 5 between the oxidation catalyst 4and the reducing agent catalyst 6.

To prevent the reducing agent spray mist 11 being forced against thewall 24 of the connecting duct 5 situated opposite the oxidationcatalyst 4 by the exhaust gas flow emerging from the oxidation catalyst4 (said wall being shown on the right in FIG. 1) and to prevent unwantedreducing agent deposits forming there, a shielding plate 20 is arrangedin front of the wall 24, in particular between the injection module 10and the wall 24. The shielding plate 20 is narrower than the connectingduct 5, with the result that some of the exhaust gas flow emerging fromthe oxidation catalyst 4 flows to the side of the shielding plate 20 (atthe top in the illustration in FIG. 1) into a buildup chamber 15 formedbetween the wall 24 of the connecting duct 5 and the shielding plate 20and produces an excess pressure (“backpressure”) there.

The exhaust gases flow out of the buildup chamber 15 through openings 16formed in the shielding plate 20 into a region on the side of theshielding plate 20 facing the oxidation catalyst 4, where they mix withthe reducing agent spray mist 11. The exhaust gas flow from the buildupchamber 15 into the region of the spray mist 11 through the openings 16is symbolized by exhaust gas flow arrows 7 c. In particular, theshielding plate 20 can be embodied as a low-cost perforated plate.

An additional baffle plate 17 can be mounted upstream, adjacent to theinjection module 10, in order to prevent dispersal of the reducing agentspray mist 11 at the collision point P of the primary jets and thus toguarantee reliable spray mist production.

FIG. 2 shows the end of the injection module 10 facing the connectingduct 5 in an enlarged partially sectioned representation. The injectionmodule 10 shown in FIG. 2 has two outlet openings 12 for the reducingagent, through each of which a reducing agent primary jet 13 emergesduring operation. Further illustrative embodiments of injection modules10 according to the invention, which are not shown in the figures, canhave additional outlet openings 12.

The primary jets 13 emerging from the outlet openings 12 collide withinthe connecting duct 5 (not shown in FIG. 2) in the region in front ofthe injection module 10. Owing to the respective momentum of the primaryjets 13, a finely atomized reducing agent spray mist 11 is produced inthe connecting duct by the collision in accordance with the “collisionbeam principle”. The reducing agent spray mist 11 produced in this waycovers the full area and is flat.

The distance d between the outlet openings 12 is less than 5 mm, inparticular less than 2 mm. Owing to the short distance d between theoutlet openings 12, the primary jets 13 in the region between the outletopenings 12 and the collision point P of the two primary jets 13 arecompact jets, which have not yet separated into individual droplets; themeeting of compact primary jets 13 optimizes the collision since eachpart of a first primary jet 13 meets a corresponding part of a secondprimary jet 13 and there are no gaps in the primary jets 13 in which nocollision occurs.

The outlet openings 12 preferably have a circular cross section sincethe jet diameter and the outlet angle of the primary jet 13 areprecisely defined in the case of a circular cross section. However, theoutlet openings 12 can also be formed with an oval cross section.

There can also be further outlet openings 12 (not shown in FIG. 2) inorder to produce additional primary jets 13, which are preferablyaligned with the same collision point P. As an alternative, there canalso be a plurality of collision points P, with which in each case twoprimary jets 13 are aligned, with the result that there is one spraymist source in the connecting duct 5 for each collision point P.

In one embodiment, the outlet openings 12 are formed in such a way thatthe primary jets 13 meet at an angle a of more than 30° in order tooptimize the collision between the two primary jets 13 and, in this way,to bring about optimum atomization of the primary jets 13, therebyensuring that a particularly fine spray mist 11 is produced in theconnecting duct 5 and the reducing agent mixes in a particularlyeffective manner with the exhaust gases in the exhaust system 22.

In one embodiment, the outlet openings 12 are formed in such a way thatthe primary jets 13 meet after a free path length L, i.e. after emergingfrom their respective outlet opening 12, of less than 10 mm, inparticular of less than 5 mm. This is a reliable way of avoiding asituation where the primary jets 13 break down into individual dropletsbefore the collision point P, which would reduce the effectiveness ofspray mist production.

The collision of two primary jets 13 which meet over their full area isillustrated schematically in FIG. 3a . The spray mist 11 produced in thecase of such a full-area collision of the primary jets 13 has anonuniform mass distribution, wherein the largest proportion of the massof the reducing agent is present in the center of the spray mist 11.

The arrows 14 show the preferential directions of flow of the dropletsproduced in the collision, wherein the length and thickness of thearrows 14 are proportional to the mass density in the respectivedirections. The mass distribution δ of the spray mist 11 is illustratedin FIG. 3a in a graphical diagram below the spray mist 11 as a functionof the position x along the width of the spray mist 11.

FIG. 3b shows a schematic graphical representation of a spray mist 11 ofthis kind, as produced with a full-area collision of the primary jets13. In the illustration in FIG. 3b , the density of the points isproportional to the mass density δ. Both in the graphical diagram inFIG. 3a and in the illustration in FIG. 3b , the increased massconcentration at the center of the spray mist 11 is clearly visible.

FIG. 4a shows the collision of two primary jets 13, which meet with anoverlap which is considerably smaller than the respective areas of thetwo primary jets 13.

A spray mist 11 produced in this way also has a nonuniform massdistribution.

In the case of a slight overlap between the primary jets, the largestproportion of the mass of the reducing agent is present at theboundaries of the spray mist 11. The arrows 14 once again show thepreferential directions of flow of the droplets produced in thecollision, wherein the length and thickness of the arrows 14 areproportional to the mass density in the respective directions. Onceagain, the mass density δ of the spray mist 11 is shown below the spraymist 11 as a diagram across the width of the spray mist 11.

FIG. 4b shows a graphical representation of such a spray mist 11,wherein the density of the points is once again proportional to the massdensity δ.

Both in the graphical diagram in FIG. 4a and in the illustration in FIG.4b , the higher mass density δ at the boundaries of the spray mist 11 isclearly visible.

FIG. 5a shows the collision of two primary jets 13 which meet with aconsiderably greater overlap than in FIGS. 4a and 4b but not with a fulloverlap as shown in FIGS. 3a and 3 b.

By virtue of the greater but not complete overlap of the two primaryjets 13, the mass of the reducing agent is carried uniformly both intothe center of the spray mist 11 and into the boundary regions thereof.The arrows 14 show the preferential directions of flow of the dropletsproduced in the collision, wherein the length and thickness of thearrows 14 are proportional to the mass density δ in the respectivedirections of flow. The arrows 14 have substantially the same thicknessand length for all directions.

Once again, the mass density δ of the spray mist 11 is shown graphicallybelow the spray mist 11 across the width of the spray mist 11. FIG. 5bshows a graphical representation of such a spray mist 11, wherein thedensity of the points is proportional to the mass density δ.

The very uniform mass distribution in the spray mist 11 is clearlyvisible both in the graphical diagram in FIG. 5a and in the illustrationin FIG. 5b , especially in a direct comparison with FIGS. 3a, 3b, 4a and4 c.

An overlap of the primary jets 13 in a range of from 30% to 70%, inparticular of from 40% to 60%, of the area of the primary jets 13 hasproven particularly suitable. With overlaps in this range, a spray mist11 with a particularly uniform mass distribution can be produced.

1-10. (canceled)
 11. An injection module (10) for injecting a reducingagent into the exhaust system (22) of an internal combustion engine (2),the injection module comprising at least two outlet openings (12) fordischarging at least one reducing agent primary jet (13) in each case,wherein the outlet openings (12) are formed in such a way that thereducing agent primary jets (13) emerging through the outlet openings(12) meet and produce a spray mist (11) in the exhaust system (22),wherein the outlet openings (12) are formed in such a way that thereducing agent primary jets (13) emerging through the outlet openings(12) meet with only a partial overlap, wherein the outlet openings (12)are formed in such a way that the reducing agent primary jets (13) meetafter a free path length (L) of less than 10 mm.
 12. The injectionmodule (10) as claimed in claim 11, wherein the outlet openings (12) areformed in a manner offset and/or tilted relative to one another.
 13. Theinjection module (10) as claimed in claim 11, wherein the overlap is ina range of from 30% to 70% of an area of the primary jets (13).
 14. Theinjection module (10) as claimed in claim 13, wherein the overlap is ina range of from 40% to 60% of the area of the primary jets (13).
 15. Theinjection module (10) as claimed in claim 11, wherein the outletopenings (12) are formed in such a way that the reducing agent primaryjets (13) meet at an angle (α) of more than 30°.
 16. The injectionmodule (10) as claimed in claim 11, wherein the free path length (L) isless than 5 mm.
 17. A section of an exhaust system (22) of an internalcombustion engine (2) having an injection module (10) for injecting areducing agent into the exhaust system (22) of an internal combustionengine (2), the injection module comprising at least two outlet openings(12) for discharging at least one reducing agent primary jet (13) ineach case, wherein the outlet openings (12) are formed in such a waythat the reducing agent primary jets (13) emerging through the outletopenings (12) meet and produce a spray mist (11) in the exhaust system(22), wherein the outlet openings (12) are formed in such a way that thereducing agent primary jets (13) emerging through the outlet openings(12) meet with only a partial overlap, wherein the outlet openings (12)are formed in such a way that the reducing agent primary jets (13) meetafter a free path length (L) of less than 10 mm.
 18. The section of anexhaust system (22) as claimed in claim 17, having a shielding plate(20), which is configured and arranged to prevent the spray mist (11)from striking a wall (24) of the exhaust system (22.
 19. The section ofan exhaust system (22) as claimed in claim 17, wherein an oxidationcatalyst (4) is arranged upstream of the injection module (10), and areduction catalyst (6) is arranged downstream of the injection module(10).
 20. The section of an exhaust system (22) as claimed in claim 17,having a shielding plate (20), which is configured and arranged toprevent the spray mist (11) from striking a wall (24) of the exhaustsystem (22), wherein the shielding plate (20) has one or more openings(16).
 21. The section of an exhaust system (22) as claimed in claim 17,wherein an oxidation catalyst (4) is arranged upstream of the injectionmodule (10), and a reduction catalyst (6) is arranged downstream of theinjection module (10), wherein the injection module (10) is arranged ina connecting duct (5) between the oxidation catalyst (4) and thereduction catalyst (6), and wherein the direction of flow of the exhaustgases is deflected by the connecting duct (5).
 22. The section of anexhaust system (22) as claimed in claim 17, wherein the outlet openings(12) are formed in a manner offset and/or tilted relative to oneanother.
 23. The section of an exhaust system (22) as claimed in claim17, wherein the overlap is in a range of from 30% to 70% of an area ofthe primary jets (13).
 24. The section of an exhaust system (22) asclaimed in claim 23, wherein the overlap is in a range of from 40% to60% of the area of the primary jets (13).
 25. The section of an exhaustsystem (22) as claimed in claim 17, wherein the outlet openings (12) areformed in such a way that the reducing agent primary jets (13) meet atan angle (α) of more than 30°.
 26. The section of an exhaust system (22)as claimed in claim 17, wherein the free path length (L) is less than 5mm.
 27. A method of injecting a reducing agent into the exhaust system(22) of an internal combustion engine (2), characterized in that themethod comprises injecting at least two reducing agent primary jets (13)into the exhaust system (22) in such a way that the reducing agentprimary jets meet with only a partial overlap in order to produce areducing agent spray mist (11) in a region of the exhaust system (22),wherein the reducing agent primary jets (13) meet after a free pathlength (L) of less than 10 mm.
 28. The method as claimed in claim 27,wherein the free path length (L) is less than 5 mm.